1. Field of the Invention
This invention relates to a method of establishing a connection between two endpoints in a communications network, and in particular but not limited to, situations where it is required to reduce the time taken to establish the connection. The invention also relates to a communications network within which this method is implemented and also to a computer program for controlling a communications network in order to implement the method.
2. Description of the Prior Art
One factor that must be taken into account during design of communications systems is that of the time taken to establish a communication session. This should be as short as possible in order that customers are not deterred from using the communications service and for applications in which communication sessions must be established without delay.
The time taken to establish a communication session is a particular issue when providing a guaranteed quality of service for transmission of internet protocol traffic. Quality of service is an important factor; customers require a good quality of service for message transmission especially for real-time applications such as video conferencing and voice. As well as this many customers require a particular level of quality of service to be guaranteed; if quality of service drops below a certain level and transmission is interrupted or noisy this may be acceptable in some situations but unacceptable in others. If particular levels of quality of service can be guaranteed this is particularly advantageous. A number of approaches to provision of guaranteed quality of service for transmission of internet protocol traffic are now described and the time taken to establish such connections discussed.
One approach that has been used is to prioritise individual transmissions that are sent over the network. For example, a system known as “DiffServ” allows messages to be marked to indicate their priority. Nodes in a communications network are then arranged to process high priority messages first. This enables high priority messages to be processed quickly but it does not provide a guaranteed level of quality of service. Also a certain amount of processing time is necessarily taken up in determining the highest priority message at a given node and this can lead to increases in the time taken to set up a communications session.
Another approach has been to reserve bandwidth over a particular route in a communications network. However, systems that use this approach (for example RSVP Resource reSerVation Protocol) typically are poor at implementing aggregation mechanisms—for example they cannot easily combine a number of separate sessions over the same route, each must have its own reservation. Another shortcoming is that they also typically only allow the called party to reserve bandwidth that is required to host a communication session. This does not allow the calling party to specify their requirements and this is problematic, especially because the calling party is typically the party which incurs costs for a call. Also, the time taken to set up reservations is often significant and can introduce delays in the time taken to establish a communications session.
Multi Protocol Label Switching (MPLS) is a standard messaging protocol that is suitable for carrying Internet Protocol traffic over communications networks such as Asynchronous Transfer Mode (ATM) networks and Frame Relay networks.
Constraint-based Routing Label Distribution Protocol (CR-LDP) is also a standard messaging protocol (CR-LDP is defined in Internet Draft: draft-ietf-mpls-cr-ldp-01.txt) that is suitable for use with communications networks that use MPLS. Mechanisms such as CR-LDP allow MPLS the ability to set-up paths between two endpoints over a list of routers, where these paths have ATM-like traffic requirements. However, there is no well-defined mechanism for the choice of the routers in this path that makes full use of the ATM-like traffic parameters. The only existing mechanism (QOSPF Quality of Service Open Shortest Path First) allows routing only in terms of advertised router speed and congestion. In tandem, QOSPF is unable to make the fullest use of CR-LDP as it cannot make use of the detailed traffic descriptions used in CR-LDP; neither can it provide detailed route information. As well as this QOSPF is not able to ensure a connection over a suggested route.
It is accordingly an object of the present invention to provide a method of establishing a connection between two endpoints in a communications network, which overcomes or at least mitigates one or more of the problems noted above.